As more and more capability is being designed into electronic components, such as memory modules and microprocessors, there are an increasing number of leads or input/output elements being placed onto electronics packages. In the past, peripherally leaded packages provided an adequate number of leads or input/output elements. Peripherally leaded packages have leads or input/output elements along the edges of the electronic component. In many applications, such packages provide an adequate number of input/output elements. In the past few years, however, there are electronic components that require more input/output elements and require packages with more densely packed leads. Grid array packaging with input/output elements placed on the surface of the components have been used to provide additional leads. There are several types of grid arrays. Ball grid arrays and chip scale packages have hemispherical solder balls as input/output elements. Land grid arrays have flat gold plated pads as input/output elements. Pin grid arrays have gold plated pins as input/output elements.
In the past, several apparatus have been used to make electrical testing connections to grid array and other semiconductor packages. Previous test contactors have had severe limitations for high performance devices and for reliable operation when used with high volume, automated device handling equipment. Many of the problems result in poor electrical performance. Typically, this is due to long electrical path lengths within the contactor. Long electrical path lengths exhibit undesirable impedance effects which interfere with the integrity of the electrical tests being performed on the device under test. Undesirable impedance effects include long paths of uncontrolled impedance. Such uncontrolled impedance paths distort high frequency signal integrity and allow crosstalk between physically adjacent paths. Other undesirable impedance effects include parasitic inductance, capacitance, and resistance. Parasitic path inductance interferes with device power and ground sourcing by inducing voltage spikes during instantaneous electrical current changes. Parasitic capacitance presents undesirable electrical loading of device and test electronics signal sources. Parasitic resistance causes voltage errors when significant current must flow through the resistive path. This is only a partial list of undesirable impedance effects which occur with long electrical paths in test contactors.
Previous test contactors often performed poorly in high volume test environments which employ automated device handling equipment. Contactor fragility often results in contactor damage when a handling equipment error presents a device to a contactor incorrectly. Contactors often wear rapidly during high volume use resulting in wear damage to alignment features and contact surfaces. Contactors may also be too susceptible to contamination from normal production environment debris such as package resin dust and package lead solder-plating.
Spring contact pins are one type of contact used to make test contactors. Inside the body carrying the contact pin is a spring. The spring interacts with long and fragile leads. Therefore, not only is electrical performance poor because of the undesirable impedance effects due to the long leads, but the life of the spring contact pin is limited due to the fragile leads.
Wadded wire contacts are another option for contacting input/output elements in a grid array. Wadded wire contacts are made of an electrically conductive spring wire material that resemble steel wool. The wadded wire contacts are small steel wool like balls or columns that are brought into contact with the input/output elements of a grid array. The problem with wadded wire contacts is that many times the small steel wool like balls take compression set early in their operating life. Each wadded wire contact in an array of wadded wire contacts can be good at manufacture or installation in the contactor but may develop a set after being compressed a few times resulting in loss of spring characteristics. The wadded wire contact arrays must undergo extensive testing before they are used. In addition, wadded wire contacts cannot be spaced closely enough together to contact the individual input/output elements on a very high density, grid array typical of chip-scale BGA packages.
Rigid contacts with an elastomer support have also been used to contact input output/elements in a grid array. A common elastomer supports an array of rigid contacts. This type of contactor has numerous problems. For example, the constant compression and decompression of the elastomer results in a continuous scrubbing of the user interface board. This causes premature board failure. In addition, the common elastomer has a different coefficient of thermal expansion than does the electronic device under test. The differences in coefficient of linear expansion values make it difficult to hold registration between the input/output elements and the device under test over a broad range of temperature. Yet another problem is poor compliancy. This system tends to require very high compression forces to accommodate non-coplanarities in electronic devices under test.
There is a real need for a contactor which can contact grid arrays that does not have the electrical performance problems of an undesirable impedance effects associated with long leads. There is also need for a contactor that has the robustness necessary for an automated test environment. There is further need for a contactor that does not depend on temperature. There is also a need for a contactor having enhanced compliance.